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What are the characteristics of a deep sea trench?
- They mark the position at which the subducting plate begins to descend beneath another plate.
- Trenches are generally parallel to a volcanic island arc.
How is a deep sea trench formed? (2 ways)
- On a destructive plate boundary where dense oceanic crust is subducted under the less dense continental crust
- On a collision plate boundary where two oceanic crusts are moving towards each other and the denser of the two is subducted, forming a trench and causing earthquakes
What are the characteristics of island arcs?
Clusters of small islands that sit in a curved line, such as the Mariana Islands
How is an island arc formed?
When two oceanic plates converge and volcanic eruptions take place underwater
List intrusive volcano features
- Volcanic plug
How is boiling mud formed?
- Boiling mud occurs when steam and gas rise to the surface under rainwater ponds.
- Acidic gases attack rocks to form clay
- Clay soil then mixes with water to produce heated mud pool.
What are the characteristics of boiling mud?
- Another type of hot spring.
- Found across the world
- Occur in very fine grained soul areas
- Appearance is determined by rainfall. In dry conditions the mud is thick and sticky, when it is raining the mud is much more fluid
Describe a batholith and explain its formation
A batholith is the largest intrusive volcanic feature, measuring 100kms in width. It contains thick and viscous lava. It is formed by several small intrusions occurring in the same place and building up.
Describe a lopolith and explain its formation
- A lopolith is a saucer shaped intrusion that is concordant to the country rock. Beneath the lopolith there will be a vertical funnel along which the magma has travelled.
- They are rare and formed by magma with a low silica content.
- Magma is forced in-between layers of sedimentary rock and crystal sagging causes the shape
Describe a laccolith and explain its formation
- Forms close to the surface and is usually concordant. Domes upwards in the centre, making rock above it dome too.
- Formed from high viscosity magma which causes a lot of pressure through feeder dyke
Describe a sill and explain its formation
A concordant intrusive volcanic feature which varies in thickness (can be 100s of metres) and can cause metamorphism. Formed in a similiar way to dykes, as magma is forced along between layers of sedimentary rock
Describe a dyke and explain its formation
A discordant intrusive volcanic feature which is formed when magma is forced along cracks or weaknesses in the rock, or when the force of the intruding magma opens up new cracks in the rock.
Describe a volcanic plug and explain its formation
If a volcano has viscous (sticky) magma then it can clog up the vent pipe of the volcano. This cools and solidifies inside the volcano, blocking it up
What landforms occur at constructive plate boundaries?
- Mid-ocean ridges
- Rift valleys
What landforms occur at destructive plate boundaries?
- deep sea trenches
- Island arcs
What landforms occur at collision plate boundaries?
Describe a mid-ocean ridge and explain its formation
Mid-ocean ridges can be found at under water divergent, constructive, plate boundaries. Underwater volcanoes erupt along the rift and can build up above sea level. Iceland was formed in this way
Describe a rift valley and explain its formation
- Where plates diverge on land, rising magma causes the continental crust to bulge and fracture forming fault lines.
- As plates keep moving apart, the crust drops down to form a valley.
- Can be 100s metres wide or deep.
- Volcanoes form around rift valleys
- E.G. The east african rift system
Describe what a hotspot is and explain its formation
- A hotspot volcano is a volcano that has formed on a plate, rather than at a plate margin.
- A hot spot is caused by a magma plume that rises up from the mantle, which forms the volcano itself. The plume remains stationary as the crust moves, forming a string of dormant volcanoes.
- An example is Hawaii
What is the case study for an LEDC volcanic eruption? When was the event?
Mount Nyiragongo in the Congo (Jan 2002)
What is the case study for an MEDC volcanic eruption? When was the event?
- Mt. Etna, Sicily
- Successive years
What is the case study for an LEDC earthquake? When was the event?
Nepal, April 2015
What is the case study for an LEDC tsunami? When was the event?
Indian Ocean, December 2004
What is the case study for an MEDC tsunami? When was the event?
Japan, March 2011